A simple explanation for this phenomenon is that CD8+ CTL do not accumulate within the eye, either because they fail to infiltrate ocular tumors or because they undergo apoptosis within the eye due to ocular expression of death inducing molecules (Griffith et al., 1995a; Yamagami et al., 1997; Hori et al., 2006). This evidence concerns the gene CD8A and eye neoplasm.